It has been commercially demonstrated that a very effective way to handle suspensions, such as paper pulp, it at medium consistency (that is about 6-15% solids consistency). When pumped, mixed, screened, and otherwise handled in this manner, significant savings in equipment, dilution liquids, and the like can be achieved. One piece of equipment that has been particularly successful in allowing handling of medium consistency suspensions is a fluidizing pump which simultaneously pumps and degassing the suspension. Typically, such pumps utilize a separate vacuum pump, piping from the fluidizing pump to the vacuum pump, a separate motor and motor mount for the vacuum pump, etc., in order to exhaust the gas that is separated from the suspension so that the suspension may be effectively pumped by the fluidizing pump impellers.
According to the present invention, it has been found that it is possible to mount a vacuum pump on the same shaft as the fluidizing pump impeller, and pull the separated gas directly into the vacuum pump. It has surprisingly been found that this can be accomplished according to the invention without redesign of the fluidizing pump impeller, change in the size of the motor for rotating the pump, or change in any other significant feature of conventional fluidizing pumps. The invention thus achieves the significant advantage of eliminating piping and an entirely separate pump, motor, motor mount, etc. with ensuing reduction in costs, and increased ease of operation.
According to one aspect of the invention there is provided a pump comprising: a main housing including a suspension inlet and a suspension outlet generally transverse to the suspension inlet; a shaft rotatable about an axis of rotation generally in alignment with the inlet; a fluidizing impeller mounted to the shaft for rotation with it, for effecting fluidization of suspension pumped by the impeller from the inlet to the outlet, the fluidizing impeller comprising a first section having impeller blades elongated in a first dimension generally parallel to the axis of rotation, and comprising second impeller blade portions extending in a dimension generally perpendicular to the first impeller blade portions, the fluidizing impeller when rotating causing gas to separate from the suspension and to collect adjacent the shaft and the second impeller blade portions; a vacuum pump including a vacuum impeller, the vacuum impeller mounted to the shaft for rotation with the shaft and the fluidizing impeller; and means defining gas passageways extending between the main housing where gas collects to the vacuum impeller, to be exhausted from the main housing, to an area remote from the main housing, by the vacuum pump. Preferably a common wall divides the fluidizing pump from the vacuum pump, with a gas passage formed in the common wall, and an annular open volume defined in that wall. A source of make-up air, controlled by a pressure responsive valve, communicates with the annular volume to provide make-up air should the vacuum pulled by the vacuum pump be greater than a predetermined amount. This avoids the possibility that suspension may be pulled in the vacuum pump if the vacuum is too high. Further, the gas exhausted from the fluidizing pump passes generally parallel to the axis of rotation and is discharged from the vacuum pump in a portion thereof opposite from the fluidizing pump. Liquid for the liquid ring of the vacuum pump is supplied through a liquid inlet, and the gas outlet defines the inner edge of the water ring. Any excess liquid from the liquid ring, and expelled gas, pass through the gas outlet.
According to another aspect of the present invention there is provided a method of simultaneously pumping and degassing a suspension having a solids content between about 6-15% utilizing a fluidizing impeller in a main housing rotatable by a shaft, and a vacuum impeller mounted on the same shaft as the fluidizing impeller. The method comprises the steps of: Feeding the suspension having a consistency between about 6-15% into operative association with the fluidizing impeller. Rotating the fluidizing impeller continuously at high speed, the impeller effecting pumping of the suspension and removing gas from the suspension, the gas tending to collect adjacent the shaft. And, withdrawing the gas from its collecting volume with the vacuum pump, the gas being pulled from the collecting volume generally parallel to the axis of rotation, through the vacuum pump past the vacuum pump impeller, and expelled from the opposite side of the vacuum pump as the fluidizing impeller.
It is the primary object of the present invention to provide for the simplified but effective removal of gas from a fluidizing medium consistency suspension pump. This and other objects of the present invention will become clear from an inspection of the detailed description of the invention and from the appended claims.